Method of operating an open-hearth furnace



Dec. 24, 1929. w. TRINKS 1,741,002

METHOD OF OPERATING AN OPEN HEARTH FURNACE Filed June 22, 1923 2 Sheets-Sheet l Hl i H 5': LJ & LL

Nl/E/V 0/? WITNESSES F 5 1 N 7 Zf7 Dec. 24, 1929. w. TRINKS METHOD OF OPERATING AN OPEN HEARTH FURNACE Filed June 22, 1925 2 Sheets-Shea. 2

Patented Dec. 24, 1929 UNITED STATES WILLIBALD TRINKS, OF PITTSBURGH, PENNSYLVANIA METHOD OF OPERATING AN OPEN-HEABTE FURNACE Application filed June 22,

My invention relates to the construction of and to the method of operation of regenerative furnaces, and centers in the construction of the passageways andports through which the combustible substances, ordinarily gas and air, gain access, to the furnace chamber and in the means and method by which the flow of these substances is controlled and by which mixture of them is effected.

The end primarily in View is the proper control of the generation of-heat, both in location and in intensity, together with the possibility of effecting variation in these matters, if desired, in accordance with the progress of the refining operation; the ultimate end is the production of refined material of the desired quality in mimimum time and at minimum expense of material and with minimum wear and tear. .While not necessarily so 1i ited, my invention is applicable to the circu stances under which I have developed it, namely to open-hearth steel furnaces fired with lean gas, such as producer gas, or blastfurnace gas, and in such application I shall in the ensuing specification describe it. It will be manifest to one reading the ensuing specification that the invention is well adapted to furnaces fired with fuels which, on account of temperature or dirtiness, cannot be put under pressure or be conducted 7 through metal pipes. :But to no such matters is the invention limited; its wider and general applicability will be understood by those skilled in the art of regenerative furnace operation.

In an application for United States L tters,Patent filed by Robert B. Kernohan and James S. Lochhead, October 29, 1920, Serial No. 420,37 7 an open-hearth furnace is shown and described, 'wherein a stream of mingled gas and air and a second stream of air alone may be directed into the furnace, the pressures being variable, and the degree of opening of certain passageways being variable,"to the end that the flame .as projected into and maintained within the furnace may be such in character as to serve best in the refining operation, and to the end that, as operation progresses, the flame may if desired be modi- 50 tied in character and suited to changing con- 1923. Serial N0. 647,008.

ditions of the furnace charge. The present invention is an improvement thereon.

In a second application of the said Kernohan & Lochhead, filed April 12th, 1922, Serial No. 551,7 81, an improvement is shown and described upon the disclosure of the application first named and to :this disclosure also my invention is applicable, and constitutes an improvement upon it.

The accompanying drawings illustrate an open-hearth furnace in the construction of which and inthe operation of which my invention may bepracticed. Fig. I is a view of the furnace in horizontal section, on the plane indicated by the broken line II, Fig. II; Fig. II is a view in vertical and longitudinal section, on the plane indicated at IIII, Fig. I.

The furnace includes the usual hearth 1, h upon which the charge is borne and where the essential refining operation takes place. Producer gas, preheated in the regenerator (not shown) flows through passageway 3; thence it rises'through vertical passageway 6, and enters from the rear the medially arranged downwardly inclined tunnel port 4; through this port the stream of gas is carried into the furnace chamber. Atmospheric air, preheated in the air regenerator (not shown) flows through passageway 2; thence it rises in divided flow through two vertical passageways 7 and 8, symmetrically arranged one on either side of the mid-line of the furnace, and enters from the rear the downwardly inclined port 5, over-arching port 4; through this port air is carried into the furnace chamber. Ducts 9 and 10 lead from ail assageways 7 and 8 and open into port 4. 8f these ducts it is to be observed that they are s mmetrically arranged, and that the ow through them will be symmetrical with respect to the mid-line of the furnace; they extend obliquely forward, and the streams flowing through them will converge with the stream flowing directly through the tunnel port 4; they open into the tunnel port 4 at an intermediate point in the length thereof, and the converging streams will mingle before the mouth of the port is reached. Nozzles 19 and 20 are provided, through which compressed air from a supply pipe 2 may be blown in jets forwardly through ducts 9 and 10. In supply pipe 21 is a valve 23 for regulating the flow, and conveniently a second valve 22, for cutting or? the flow entirely.

In the operation of open-hearth furnaces as commonly conducted hitherto, the draft through the furnace has been relatively feeble and combustion has been imperfectly controlled. This has been particularly true of furnaces fired with producer gas. The air ordinarily has been drawn through the regenerator and into the furnace merely by the stack effect of the regenerators and uptakes, and only such pressure has commonly been exerted upon the gas as is incident to delivery through a supply pipe. In some cases a blowing fan has been placed in the stream of air supply to the furnace, but there is a practical limitation upon the building up of pressure there; when the pressure exceeds a small amount, leakage through the masonry of the furnace structure becomes too great. It is impossible, because of expansions and contractions incident to service, to build a furnace which shall be tight against such leakage. And there is another difficulty to be dealt with. High pressures and high ve locities, very desirable in order to produce a sharp flame, require that the ports be relatively narrow; and narrow ports do not afford at the discharge end of the furnace unhindered exit for the products of combustion. (It is of course to be understood, as is intimated at the beginning, that I here am considering an open-hearth furnace of the preva lent regenerative type, in which the flow of the flame is periodically reversed, and in which the same ports serve alternately for the inflow of gas and of air and for the outflow of the products of combustion.) Because of these difficulties chiefly, and in spite of various relief projects, open-hearth operation has as a matter of practice been limited to low rates of flow of air and of gas and to the generation of a consequent long and lazy flame. This flame is still burning when it reaches the ports-at the outgoing end of the furnace, and combustion continues through the ports and even down into the regeneratorsa state of things both wasteful and destructive.

The proposal to use dampers for reducing the effective size of the passageways on the intake end of the furnace, and for so increasing velocity of flow, involves complication of structure, and dampers when present absorb a great deal of heat.

In the operation of my improved furnacedescribed above, compressed air is blown through nozzles 19 and 20 into ducts 9 and 10. This compressed air may be preheated or not, as found desirable or convenient. The jets of air issuing from the nozzles have high velocity-from 600 to 1400 feet per second, a matter conditioned upon the actual pressure of the supply and upon the shape of the nozzle and the size and shape of the orifice. This high-velocity jet entrains hot air from the uptake passages 7 and 8, and induces a flow of air through ducts 9 and 10 into the stream of gas advancing through port t. Thus the entering stream of air is divided: one .portion is directed into port 4, where it mingles with the gas before entering the furnace chamber; the other portion flows unmingled through port 5 into the furnace chamber. The relative value of these two portions of the stream of entering air is variable and responsive to the degree of opening of regulating valve 23; if that valve be closed completely, .all of the air will enter the furnace chamber through port 5and, indeed, because of the fact that in the absence of special apparatus to establish a different condition of things, the gas advances to the furnace under pressure greater than that of the air, there will be some back flow of gas from port 4 through ducts 9 and 10 and into the streams of air advancing to port 5. As valve 23 is gradually opened, such back flow of gas first is stopped, andthen streams of air are directed forwardly through ducts 9 and 10 into the stream of gas in port 4. These streams of vair increase in volume, and the streams flowing to port 5 correspondingly decrease, as valve 23 is opened wider. Ordinarily from one tenth to one fifth by Weight of the air flowing in ducts 9 and 10 is that which flows from the nozzles; the rest isdraWn in from the streams of air rising through uptake passages 7 and S. By-properly proportmnzng in size ports 4 and 5, passageways 7 and 8, and ducts 9 and 1-0, it is possible by the means decribed to divert through ducts 9 and 10 into port 4 any desired fraction of. the streams of air risingthrough uptake passageways 7 and 8. Indeed it is possible so to divert substantially the 7 whole of these streams; ordinarily it is not desirable in operation to go so far as that, but it is preferable to allow some air to enter the furnace through port 5.

lVhen valve 23 is nearly closed the flame is long and lazy such a flame in fact as is usual in opcn-hearth operation as commonly conducted hitherto; if the valve 23 is opened, the flame is short and sharp. Any desired sharpness of flame may be obtained by movement of the regulating valve 23. A shorter sharper flame than that usual in the open-hearth operation is desirable; combustion is effected within the furnace chamher, where alone combustion is desired, and the passageways and regenerators through which the outflowing gases pass are not subjected to the destructive action of combustion in progress Within them. Furthermore, reg ulation by valve 23 makes possible variation in quality of flame (if such variation be desired) according to the progress of the re fining operation: at the beginning of a run the flame may be relatively shortand sharp, and toward the end relatively long and lazy.

I have shown the compressed air supply pipes 21, together with the connections which terminate in nozzles 19 and 20 to be suspended, as by chains 24, and it will be understood that by such means the nozzles 19 and 20, positioned as shown at the intake end of the furnace, may at the outtake end he swung aside, away from the deleterious influences of the outfiowing products of combustion. As an alternative expedient, these pipes may be 'stationary and the nozzles water-jacketed an expedient so well known in the general field of furnace structure as to require no illustration.

I have said, in speaking of the intake end of the furnace, that as the valve 23 is gradually opened, back fiow of gas from port 4 through ducts 9 will be stopped. Correspondingly, at the outgoing end of the furnace, the maintenance of jets of air from nozzles 19 and 20 of properly regulated intensity will be effective to prevent the products of combustion from streaming through ducts 9 and 10, and this in particular cases will be a matter of value.

The showing afforded in the drawings will be understood to be diagrammatic, and particularly in these respects :The ducts 9 and 1.0 are shown as rectangular in cross section and uniform in dimensions throughout their extent. Manifestly they may be particularly shaped according to the teaching of pneumatics to afford in highest degree the effect described; the nozzles 19 and 20, shown diagrammatically as mere tapered terminations of the feed pipes protruding into the ducts, may be elaborated and refined in form; they may be made of the multiple-jet type; they may in position be so related to the form of the ducts as best to achieve their effect; again, the openings through the walls of passage-ways 7 arid 8, through which the nozzles 19 and 20 are. shown to be movable are, in order that the structure may be clearly understood, shown diagrammatically as greater in dimensions than in actual building they would be.

As shown in the drawings, the furnace-reversing instrumentalities are arranged for the inflow of gas and air at the left-hand end and for the outflow of products of combustion at the right-hand end. At the right-hand end of the furnace the valve 22 in the supply pipe 21 is closed and the pipe itself is retracted and the nozzles 19 and 20 are withdrawn be yond the walls of vertical passageways 7 and 8. At the left-hand end the pipe 21 is advanced, the nozzles-19 and 20 are in position in ducts 9 and 10, and valve 22 is open. Gas and air are entering through the ports at the left-hand end and are burning in a flame which sweeps from left to right, and the products of combustion are escaping through the ports and passageways at the right-hand end. At proper intervals of time the furnace is reversed and, incidentally to reversal, the pipe 21 and nozzles 19 and 20 which had been retracted are advanced, those which had been advanced are retracted, valve 22 of the now advanced pipe 21 is opened while the corresponding valve in the now retracted pipe has on retraction been closed. (Apparatus for effecting reversal of the furnace requires no illustration, and I have not sought to afford illustration of it.) As has already been explained, the degree of opening of valves 23 may if desired 'be diminished as operation upon a given furnace charge progresses, to the end that at the beginning the flame may be relatively short and sharp and toward the end relatively long and lazy.

As has been intimated, I do not intend ordinarily to resort to special means for building up pressure on air or gas on the intake end of the furnace nor to special means for drawing the products of combustion out from theoutgoing end. Nevertheless, the practice of my invention does not forbid the use of such ancillary apparatus, if for any reason it be found desirable.

The jets of air entering port 4 through ducts 9 and 10 produce combustion in port 4, to the extent that the air and gas mix. Mixture, however, is not complete until the gases have just left port 4 on their way tothe furnace. In consequence, combustion in and just beyond the opening from port 4 is so rapid that an extremely high temperature is attained, in spite of the injection of cold or only slightly preheated air through nozzles .19 and 20. Preheating of this injected air may of course be resorted to, and may be carried to any degree, but ordinarily preheating will not be necessary.

An advantage of projecting streams of air at relatively high pressure-through ducts 9 and 10 and forwardly into port 4 is found in an increased flow of gas, and that without an otherwise requisite increase of pressure in the gas uptake passageway 6. A jet of air under high pressure projected ,from the nozzle into the duct has great kinetic energy, and entrains or induces the flow of large weights of air (five to ten times as much as issues in the jets) from the air passageways 7 and 8 through ducts 9 and 10 into port 4. Furthermore, by the use of the jets of compressed air, this projecting of streams of air through ports 9 and 10 is attained without subjecting the furnace structure to augmented pressure in the regenerators or in the air uptake passageways 7 and 8, and without resort to dampers.

I have consistently throughout the specification spoken of the substance projected through nozzles 19 and 20 as compressed air, and ordinarily compressed air will be best; air is requisite to combustion in ordinary practice, and is one component of the com bustible mixture within the furnace chamber. But manifestly the jet might be constituted of some other fluid of steam, for example, or of oxygen, or of a substance which, not entering into the act of combustion, still serves mechanically, to divert the substance of one, of the two streams through the ducts 9 and 10 into the other stream. The arrangement of ports andpassageways might be reversed, and gas rising through passageways 7 and 8 divertedand projected into the air advancing from passageway 6 through port 4. v

I claim as my invention:

1. In a regenerative furnace including in its structure the combination of a. furnace chamber, an air passageway opening from regencrator through an air port to said furnace chamber, a duct branching from said passageway and opening through a second port to said furnace chamber, means for projecting a jet of fluid longitudinally of said duct toward said second port, and means for supplying with fuel the stream flowing through said second port, the method of operation herein described which includes the maintenance on the outgoing end of the furnace of a jet of fluid from said jet-projecting I means, whereby the outgoing stream of gases is diverted from said second port to said air port.

2. The method herein described of operating an open-hearth furnace which consists in causing air to flow under low pressure from regencrator through air port to furnace chamber and products of combustion from furnace chamber through regenerator to stack and in impelling under a jet of fluid and at accelerated rate of flow a branch stream from the main stream of air at the inlet end of the furnace through a second port into the furnace, and supplying fuel to such stream, while at the same time at the outlet end of the furnace maintaining a corresponding jet of fluid and thereby excluding the products of combustion at the outgoing end of the furnace from passage through the second port.

In testimony whereof I have hereunto set my hand.

WILLIBALD THINKS. 

